This invention relates to an apparatus and method for use in measuring the viscosity of a liquid. In one application, the apparatus and method can be used to measure the viscosity of a dense medium such as a suspension of ferrosilicon in the art of diamond recovery, the term "liquid" being intended to include suspensions.
Up to now, viscosity measurements have usually been made in a laboratory under controlled conditions. This involves the extraction of a sample of the liquid to be tested, and the introduction of the sample to an independent apparatus. One such apparatus is described in the specification of U.K. patent application No. 174377/77. Here, the sample is pumped upwardly in one limb of a U-shaped chamber past a bobbin arranged to rotate in the liquid. The motor driving the bobbin is either set to rotate the bobbin at constant angular velocity, or to draw constant current. In the former case, the current drawn is monitored, and used to give an indication of viscosity in terms of a known relationship between current drawn and drag on the bobbin, which in turn is dependent on viscosity. In the latter case, the motor speed, which is dependent on the drag on the rotating bobbin and hence on the viscosity of the liquid, is monitored to give an indication of viscosity.
The main disadvantage of an apparatus of this nature is that it is necessary to take periodic samples from the medium as it flows around its circuit. Continuous monitoring is not possible. A further disadvantage is that, if the apparatus should fail to operate, the liquid sample under test will merely remain in the apparatus. In a case where the liquid is a dense medium such as a suspension of ferrosilicon, this can result in clogging of the apparatus and wastage of time in clearing it for re-use.